Astrocytes are critical for maintaining brain homeostasis through metabolic support, neurotransmitter regulation, and blood–brain barrier integrity. In the aging brain and neurodegenerative conditions, astrocytes undergo functional and morphological changes that culminate in a state of cellular senescence. Astrocytic senescence—characterized by irreversible cell-cycle arrest and a pro-inflammatory senescence-associated secretory phenotype (SASP)—is emerging as a key contributor of chronic neuroinflammation and synaptic dysfunction in aging. This review examines the molecular mechanisms underlying astrocyte senescence, highlighting how persistent DNA damage responses (DDR), oxidative stress, and mitochondrial dysfunction disrupt essential astrocytic functions (e.g., glutamate uptake, K⁺ buffering, and metabolic coupling with neurons). These senescent changes in astrocytes lead to impaired synaptic plasticity and contribute to age-related cognitive decline. Collectively, astrocytic senescence represents a pivotal and targetable mechanism in age-related neurodegeneration, and therapeutic strategies aimed at eliminating senescent cells or modulating the SASP hold promise for restoring synaptic function and promoting healthy brain aging.

Tunneling nanotubes (TNTs) are dynamic cell surface conduits that enable direct transfer of ions, signaling molecules, and organelles. They have emerged as a key mechanism of intercellular communication, complementing classical pathways such as synapses and paracrine signaling. In the central nervous system (CNS), TNTs exhibit a functional duality, particularly under aging and stress, where TNT-mediated exchange may shift from protective to maladaptive. On one hand, TNTs support homeostatic functions, ranging from mitochondrial transfer to stem cell-mediated rescue and astrocyte–neuron metabolic support. On the other hand, they facilitate the spread of prions and neurodegenerative protein aggregates, such as Tau and α-synuclein, with astrocytes playing a regulatory role. Despite rapid advances, TNT research faces challenges from conceptual heterogeneity and experimental standardization, especially in complex tissues such as the CNS. Recent mechanobiological and bio-inspired approaches, including force-based assays and three-dimensional culture models, provide new insights into TNT formation, stability, and cargo transport, extending beyond neural systems. This review offers an integrative synthesis of molecular, structural, and mechanobiological principles underlying TNT-mediated communication, emphasizing astrocyte–neuron crosstalk, while proposing validation criteria to support rigor, reproducibility, and cross-study comparability. TNTs thus emerge as dynamic, context-dependent interfaces with broad relevance to neurodegeneration, cancer, and biomedical applications.